Certificate of Sponsorship Explained: Defined vs Undefined, Costs and Timing

A Certificate of Sponsorship — almost always abbreviated to CoS — is not a certificate in any physical sense. It is a numeric reference generated inside the Home Office’s Sponsorship Management System by an employer that already holds a sponsor licence. Each CoS is unique to a single role offered to a single named worker, and one must be assigned before that worker can submit a Skilled Worker, Health and Care, or other sponsored visa application.

Defined vs Undefined

Two kinds of CoS exist, and the distinction mostly matters to the employer:

• Defined CoS — used when the applicant is outside the UK. The employer applies to the Home Office for permission to issue each defined CoS individually. The published service standard is one working day.
• Undefined CoS — used when the applicant is in the UK switching from another visa. The employer holds an annual allocation and can assign one immediately, with no Home Office approval step.

From the applicant’s perspective there is no operational difference: both produce a 12-character reference used to start the visa application. If an out-of-UK offer is being delayed, the commonest reason is that the employer is waiting on Home Office defined-CoS approval.

Costs

The employer pays a CoS assignment fee directly to the Home Office at the moment of issue. Verify the current figure against GOV.UK before relying on it.

The employer must also pay the Immigration Skills Charge (ISC) up front for the full length of the sponsorship — £1,000 per year for medium and large employers, £364 for small or charitable sponsors. Charities and certain occupations are exempt.

Under the published Home Office rules these fees are payable by the sponsor, not the applicant. See our guide on spotting fake sponsorship offers for the verification steps that catch CoS-for-sale fraud.

What the CoS must say

A valid CoS includes the applicant’s name, the role title, the relevant SOC 2020 code, the salary, the working hours, the start and end dates, and a short job summary. The salary on the CoS is the figure the Home Office scores the application against — not the range advertised on the job listing. If the figure on the CoS is below the relevant threshold, the application is refused regardless of what the offer letter said.

The most common errors on a CoS are the wrong SOC code, the wrong salary, and a start date that does not match the intended travel. Applicants typically review their CoS carefully before submitting the visa application and ask for a correction if any field is off.

Validity and travel

A visa application must be submitted within three months of the CoS being assigned. If the window is missed, the CoS expires and the employer must issue a new one — incurring the fees again.

Once a visa has been granted, the holder can travel to the UK up to fourteen days before the CoS start date, but no earlier.

What can go wrong

• Wrong SOC code on the CoS. The most common reason for refusal — it changes the going rate, often pushing the offered salary below the threshold.
• Salary mismatch. The CoS salary and the contract should match. If they do not, the Home Office uses the lower figure.
• Sponsor licence suspended after issue. Rare but not unheard of. The CoS becomes unusable until the licence is reinstated; see Sponsor licence status for the available paths.

Frequently asked questions

Is a Certificate of Sponsorship a physical document?

No. It is a 12-character reference number generated in the Home Office's Sponsorship Management System and shared with the applicant by the employer, normally by email.

What is the difference between defined and undefined CoS?

Defined CoS are used for applicants outside the UK and require Home Office approval for each one (usually within one working day). Undefined CoS are used for in-UK switches and come from the employer's annual allocation; they can be assigned immediately.

How long is a CoS valid for?

A visa application must be submitted within three months of CoS assignment. If that window expires the CoS lapses and the employer must reissue.

Who pays for the CoS?

The employer pays both the CoS assignment fee and the Immigration Skills Charge to the Home Office. Under the published rules, neither fee is payable by the applicant.

What is the most common reason a CoS leads to refusal?

A SOC code mismatch — usually a code that produces a going rate higher than the offered salary. The Home Office reads the salary on the CoS itself; if the CoS figure falls below the threshold, the application is refused regardless of what the offer letter says.